Hornwort

Ceratophyllum demersum

Also known as Coontail, Rigid hornwort

FreshwaterBrackishStemCuttingsSide shoots

Hornwort (Ceratophyllum demersum) — Totodilefan · Public domain

Care at a glance

Light: Low light
CO2: No CO₂ needed
Growth rate: Fast
Placement: Floating
Type: Stem
Temperature: 59–86°F (15–30°C)
pH: 6.0–7.5
Hardness: 5–15 dGH
Max height: 39.4 in (100 cm)
Spread: 5.9 in (15 cm)
Nutrient uptake: Water column
Growth region: Submersed
Difficulty: Beginner
Origin: Cosmopolitan (native to all continents except Antarctica)
Family: Ceratophyllaceae

Overview

About as forgiving as aquarium plants get: it needs no substrate, no CO2, and only low light, so you can float it, wedge a bundle behind decor, or weigh a stem down with a plant weight. Because it feeds entirely from the water column it is excellent at soaking up ammonia and nitrate, which makes it a go-to for cycling tanks and shrimp setups. To propagate, just snip or pinch off a side shoot and let it grow. The one habit to expect is needle-drop: after a move or a parameter swing it can shed leaves and leave bare stems, but it usually pushes new growth from the tips within a week or two.

In the wild

Found worldwide in still and slow-moving fresh water, from ponds and lakes to ditches and slow rivers, on every continent except Antarctica. It lives fully submersed and rootless, drifting in the water column or loosely anchored in soft sediment by pale modified leaves rather than true roots.

Good to know

The sole surviving genus of the family Ceratophyllaceae, an ancient lineage that sits near the very base of the flowering plants. It has no roots at all and takes everything it needs straight from the water through its foliage. The genus name comes from the Greek for horn and leaf, a nod to the stiff, forked, antler-like whorls of leaves that crowd toward the stem tips.

Did you know

Hornwort is allelopathic, meaning it releases compounds into the water that suppress algae and even slow down competing plants, which is part of why a healthy clump keeps a tank so clear.